THE NUTRITION OF THE HEART 165 



respiration being maintained throughout the experiment. The chief source of difficulty 

 with the preparation is edema of the lungs. This occurs much more readily with the 

 lung of the cat than that of the dog. Analysis of the alveolar air in the preparation 

 gives information of great value regarding the nature of the gaseous metabolism of the 

 heart (consumption of oxygen and respiratory quotient), and by altering the CO^ eon- 

 tent of the inspired air, the influence of changes in H of the perfusion fluid can be ob- 

 served (Evans '* 9 ). 



RESUSCITATION OF THE HEART IN SITU 



A suitable intracoronary pressure is a sine qua non for the mainte- 

 nance of the heartbeat, and this is a fact of great clinical significance, 

 for it indicates that any attempts to resuscitate a dead animal are cer- 

 tain of failure unless the method is such as will bring a nutrient fluid 

 under a certain pressure to bear on the coronary arteries. Injection of 

 fluid, even of defibrinated blood, into a vein will obviously fail to ful- 

 fill this condition, for the perfusion must be made into an artery so that 

 the fluid is carried down the aorta and thence into the coronary arteries. 



The practical question, in so far as resuscitation of the heartbeat is 

 concerned, is therefore, How can we get the necessary fluid under pres- 

 sure into the beginning of the aorta? Even if we were to transfuse fluid 

 under considerable pressure into the aorta through the carotid artery, 

 it would mainly follow the large vessels leading away from the heart, 

 only a fraction of it reaching the beginning of the aorta. To compel the 

 fluid to pass towards the heart we must introduce some obstruction to 

 its passage peripherally. This can be done by the injection of a consid- 

 erable dose of epinephrine (adrenaline) in normal saline solution through 

 the needle of a hypodermic syringe inserted into the tubing leading 

 from the burette or pressure bottle to the cannula in the carotid artery. 

 As the perfusion fluid is running in, the epinephrine injection is quickly 

 made, artificial respiration and cardiac massage being meanwhile prac- 

 ticed. In the majority of animals it will be found that complete res- 

 toration of the normal blood pressure can be effected by this method. 

 Indeed by performing the resuscitation under aseptic conditions, some 

 animals may be permanently resuscitated so far as the circulation is 

 concerned, although the nervous structures, even after a few minutes 

 of " death," never reacquire their normal condition. 



The epinephrine acts mainly by constricting the small arterioles and 

 thus directing the bloodflow towards the heart, but partly also by a direct 



I stimulating action on the cardiac muscle. It does not, however, con- 

 tract the coronary vessels; on the contrary, it is said to cause these 

 slightly to dilate. 



